After adding a new constraint,the whole rig is broken
change the pole angle in the IK constraint to have it pointing toward the pole target, you have to eyeball it.

Quadripedal Rigging: Twisted limbs

https://vimeo.com/171279647

The reason why the person in the tutorial didnt need to do it was probably because their bones had a different role angle (select bone in edit mode Ctrl R and rotate it) or the bones have a different rotation mode (select bone in pose mode, go to properties editor->bone->transform->rotation mode)